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The morphological and functional development of the digestive system in meagre ( Argyrosomus regius, Asso, 1801) was described by means of histological and enzymatic approaches in order to provide insight into the digestive physiology of the species at early life stages of development and evaluate whether the acquisition of digestive capacities matched the morphological development of digestive organs. For this purpose, A. regius were reared from hatching to the juvenile stage at 18 °C using a standard feeding sequence of enriched rotifers (2–15 days posthatching, dph), Artemia metanauplii (14–51 dph) and microdiet (35–51 dph). Histological and enzymatic analyses indicated that A. regius larvae had at the onset of exogenous feeding (2 dph, 3.2 ± 0.1 mm in standard length, SL) a well differentiated exocrine pancreas, and bile salt-activated lipase and alkaline proteases being the main pancreatic enzymes involved in food digestion. Ontogenic changes in pancreatic enzymes occurred between 3.2 and 3.9 mm in SL, coinciding with the resorption of the oil globule and the complete transition to exogenous feeding, and between 4.2 and 5.8 mm in SL (20–25 dph). Regarding acid digestion, pepsin was not detected in A. regius until 6.0 and 6.8 mm in SL (31 dph), coinciding with notochord flexion and the progressive decrease in the activity of alkaline protease and leucine-alanine peptidase (intestinal cytosolic enzyme) activities, indicating a shift in the mode of digestion. The detection of pepsin activity in A. regius occurred after the appearance of the first gastric glands (4.6 and 5.8 mm SL). Thus, authors need to be cautious when extracting conclusions about the beginning of acid digestion and the onset of weaning of larvae just using histological data, since it has been shown that morphology does not match functionality with regards to the stomach. The comparison of present results with other studies conducted in this species using different rearing conditions ( e.g. mesocosm technique, larval density, water temperature, feeding sequence) indicated that the functional development of the digestive system in A. regius assessed by the activity of alkaline and acid proteases is a well-conserved process that generally occurs within a range of body size regardless of larval age and rearing conditions. Thus, authors recommend using morphometric and/or morphological variables ( e.g. length, developmental stage) together with the age of larvae expressed in days after hatching for comparative purposes among different studies. Statement of relevance The morphological and functional development of the digestive system in meagre ( Argyrosomus regius ) was described by means of histological and enzymatic approaches in order to provide insight into the digestive physiology of the species at early life stages of development. Combining histological and enzymatic analytical procedures we evidenced that stomach's functionality did not match its morphological organization, since pepsin activity was not detected until some days after the appearance of the first gastric glands. This indicates that authors need to be cautious when extracting conclusions about the beginning of acid digestion and the onset of weaning of larvae just using histological data. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of diets with different plant protein ingredients on proximate composition, tissue metabolites and tissue fatty acid composition, as well as hepatic and intestinal histological modifications in Senegalese sole ( Solea senegalensis). Fish (21.5 ± 2.8 g body weight) were fed six isonitrogenous and isoenergetic diets during 11 weeks. A control diet containing fish meal as the main protein source was compared with five experimental diets replacing 30% fish meal protein by different plant protein sources: soybean meal ( SBM), soybean protein concentrate ( SPC), soybean protein isolate ( SPI), wheat gluten meal ( WGM) or pea protein concentrate ( PPC). The inclusion of different plant protein did not significantly affect growth and proximate composition of fish. The hepatosomatic index was not significantly different to the control group; however, utilization of WGM significantly increased hepatocyte size. Plasma protein values and muscle triglycerides were influenced by the inclusion of SBM and WGM in the diets respectively. Feeding fish on SBM, WGM and PPC diets significantly enhanced n-6 fatty acid levels in muscle, particularly linoleic acid. None of the plant protein ingredient used in the diets decreased arachidonic, eicosapentaenoic as well as docosahexaenoic acid values in liver and muscle. Overall, histological studies did not reveal the existence of any intestinal alterations induced by the inclusion of different plant proteins. Despite moderate changes produced by SBM, SPC and WGM, inclusion of dietary plant protein ingredients has no major impact on growth, tissue and blood biochemistry, fatty acid profile and gut integrity of Senegalese sole juveniles. [ABSTRACT FROM AUTHOR]

The digestive tract of Trachelyopterus striatulus (Steindachner, 1877) was studied using morphological, histological, and histochemical techniques. The barbels, lips and tongue had stratified squamous epithelium with mucous, claviform cells, and taste buds. Trachelyopterus striatulus had a dental plaque with villiform teeth. The bucopharyngeal cavity was formed by the gill apparatus and pharyngeal teeth with vilifform denticles. The oesophagus presented stratified squamous epithelium with mucous cells and taste buds. The stomach included cardiac, fundic, and pyloric regions and a simple prismatic epithelium with prismatic cells that reacted positively to periodic acid-Schiff (PAS) and amylase+PAS. Only the cardiac and pyloric regions responded positively to alcian blue pH 2.5 (Ab pH 2.5) and alcian blue pH 0.5 (Ab pH 0.5). The cardiac and fundic regions exhibited tubular gastric glands. The intestine was 118.90 ± 22.49 mm long with an intestinal coefficient (CO) of 0.83 ± 0.13. The epithelium was simple prismatic with a brush border and goblet cells, and a greater number of goblet cells were found in the caudal region of the intestine. The mucous cells and goblet cells reacted positively to PAS, amylase+PAS, Ab pH 2.5, and Ab pH 0.5. We analysed if the function of the mucosubstances and morphological characteristics of the digestive tract of T. striatulus are compatible with omnivorous feeding habit. [ABSTRACT FROM AUTHOR]

In this work, several features during the wedge sole larval development have been described. The newly hatched larva presented an acidophilic yolk with some oil drops. The digestive tract began to differentiate at 1 DAH, with a loop being discernible. The pancreas and liver were completely formed at 2 DAH, the former showing its typical basophilic acinar structure and acidophilic zymogen granules. The first supranuclear vesicles in enterocytes were seen at 3 DAH. At 4 DAH, yolk reserves were completely exhausted, the number of oesophagus and intestine mucous cells increased, and the heart was differentiated into four chambers: the venous sinus, atrium, ventricle, and arterious bulb. The development was fast and almost all organs were differentiated at 2 DAH. It is important to emphasize that gastric glands were not detected, a factor that should be considered when deciding diet formulation and feeding strategies for the rearing of this species. [ABSTRACT FROM AUTHOR]

The article presents a summary of a study on the peculiarities of oro-pharyngeal cavity of rainbow trout fish. It shows that the oro-pharyngeal cavity, which represents the first section of the digestive tract in fish, has some morpho-histological peculiarities in terms of shape and of couple anatomical segments. It also characterizes the morphological and histological attributes of the said segment of the fish's digestive system.